QCA7e_ch02_szb_handouts

QCA7e_ch02_szb_handouts - Daniel C. Harris Quantitative...

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1 Quantitative Chemical Analysis Seventh Edition Quantitative Chemical Analysis Seventh Edition Chapter 2 Tools of the Trade Daniel C. Harris Daniel C. Harris Topics in this chapter • Basic laboratory apparatus and manipulations –Sa fe ty – Notebook –Mass : Balance –Vo lume :
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2 The smallest scales
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3 Safety • Eye protection - goggles • Close heel and toe shoes • Avoid bare legs and arms – lab coat • Use gloves when appropriate • Wash gloved hands before removing gloves • Use fume hood • Label all vessels to indicate what they contain • Dispose of waste properly
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4 • Write clearly • Setup notebook for numerical data before lab • Show ALL calculations and include units • Record complete file spec for all computer files • You may want to have sections on: – The purpose - Write chemical equations – The methods used – Results (experimental data) – Conclusions • Most important: – be able to reproduce from your notes Lab Notebook The analytical balance • Displacement of the balance pan generates a correction current. The electromagnet then restores the pan to its initial position. N and S are the north and south poles of the permanent magnet.
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5 Calibration of the Balance • Analytical balances calibrate themselves automatically with a standard mass on the load-bearing structure • Less expensive electronic balances are calibrated at the factory – gravity may not be the same as the force of gravity in your lab • Periodically check your balance by weighing a standard mass. Balance weights
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6 Buoyancy Buoyancy is the upward force exerted on an object in a liquid or gaseous fluid. • An object weighed in air appears lighter than its actual mass by an amount equal to the mass of air that it displaces. • Buoyancy error occurs when the density of the object being weighed is not equal to the density of the standard mass. Buoyancy Correction • If mass m ’ is read from a balance, the true mass m of the object weighed in vacuum is given by: d a is the density of air (0.0012 g/mL near 1 bar and 25 ° C) w is the density of the calibration weights (typically 8.0 g/mL) is the density of the object being weighed
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7 Example Buoyancy Correction Calculation • A pure compound called “tris” is used as a primary standard to measure concentrations of acids. The volume of acid required to react with a known mass of tris tells us the concentration of the acid. Find the
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This note was uploaded on 01/29/2009 for the course CHEM CHEM 141 taught by Professor Balintsztaray,ph.d during the Fall '08 term at Pacific.

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QCA7e_ch02_szb_handouts - Daniel C. Harris Quantitative...

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